Lymphocyte-specific genetic instability and cancer

On the long-term effects of methyl isocyanate on cell-mediated immunity in Bhopal gas-exposed long-term survivors and their offspring

Methyl isocyanate (MIC) is a toxic industrial chemical that is documented as a potent respiratory toxicant. We investigated cell-mediated immunity (CMI) in the MIC-exposed long-term survivors and their offspring born after the Bhopal gas-leak tragedy in 1984. Several earlier reports show inconsistency in the assessment of immunological effects of MIC on the human population. In these studies, important factors including lifestyle attributes were overlooked. We incorporated these factors also in our study of the basic cell-mediated immune function in the Bhopal MIC-affected population. Twenty-seven years after exposure, we assessed the circulating T-lymphocyte frequency using E-Rosette assay. A total of 46 MIC-exposed healthy long-term survivors and their offspring were studied vis-a-vis parallel gender–age group-matched unexposed controls from Bhopal and various other regions of India. The influence of several lifestyle variabilities (smoking, alcohol intake, and tobacco chewing) on T-lymphocyte frequency was also taken into consideration. Our observations suggest that Erythrocyte-Rosette-forming cell (E-RFC) distribution frequency is largely insignificant in the MIC-affected population as compared to controls ( p > 0.05). In the MIC-affected tobacco chewers, there was a trend of suppression in CMI (relative decrease = 10.3%) as compared to nonchewers. Overall, our results show negligible long-term effect of MIC on CMI measured in terms of E-RFC frequency. These observations are not in agreement with earlier findings that immunosuppressive effects of MIC exposure persist in the T-cells of the affected population. However, atypical lymphocytes were frequently observed as E-RFC in the exposed females when compared to all other subgroups. Hematopoietic disorders (atypical lymphocytosis) in the MIC-affected population along with previous reports on the cytogenetic and humoral immune system linking cancer risk and chronic obstructive pulmonary disease (COPD) are important.

Cytogenetic instability in young patients with multiple primary cancers

Patients younger than 45 years with multiple cancers and a family history of cancer were identified and examined for cytogenetic instability. The cohort included 50 individuals: 19 patients suffering from at least 2 independent cancers, 11 healthy control individuals, a positive control group of 5 highly radiosensitive patients (>grade 3, RTOG), and a tumor control group of 15 patients with a single tumor. Peripheral blood lymphocytes were irradiated in vitro (0.7 Gy, 2.0 Gy). Metaphase chromosomes 1, 2, and 4 were labeled by means of 3-color fluorescence in situ hybridization. Chromosomal aberrations (breaks per metaphase [B/M], complex chromosomal rearrangements [CCR/M]) were analyzed. Very high levels of chromosomal aberrations were detected in a "core group" of 5 patients. These patients displayed much higher rates of B/M and CCR/M than controls. Ten patients had moderately elevated chromosomal aberrations and 4 patients were indistinguishable from controls. We conclude that a significant proportion of young patients with multiple tumors and a family background of cancer display cytogenetic instability.

Quantitation of aberrant interlocus T-cell receptor rearrangements in mouse thymocytes and the effect of the herbicide 2,4-dichlorophenoxyacetic acid

Small studies in human populations have suggested a correlation between the frequency of errors in antigen receptor gene assembly and lymphoid malignancy risk. In particular, agricultural workers exposed to pesticides have both an increased risk for lymphoma and an increased frequency of errors in antigen receptor gene assembly. In order to further investigate the potential of such errors to serve as a mechanistically based biomarker of lymphoid cancer risk, we have developed a sensitive PCR assay for quantifying errors of V(D)J recombination in the thymocytes of mice. This assay measures interlocus rearrangements between two T-cell receptor loci, V-gamma and J-beta, located on chromosomes 13 and 6, respectively. The baseline frequency in four strains of mice was determined at several ages (2-8 weeks of age) and was found to be stable at approximately 1.5 x 10(-5) per thymocyte. Strain AKR, which has a high susceptibility to T-cell lymphomas, did not show an elevated frequency of aberrant V(D)J events. We used this assay to examine the effects of the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) on the frequency of these events. Female B6C3F1 mice, 27 days of age, were exposed to 2,4-D by gavage at doses of 0, 3, 10, 30, and 100 mg/kg/day for 4 successive days and sacrificed on day 5. Thymus DNA was isolated and examined for illegitimate V(D)J recombination-mediated gene rearrangements. In addition, pregnant mice were exposed to 2,4-D and thymocytes from the offspring examined at 2 weeks of age. No significant increase in aberrant V(D)J rearrangements was found, indicating that under these conditions 2,4-D does not appear to effect this important mechanism of carcinogenesis.

Genetic disorders associated with cancer predisposition and genomic instability

Genomic instability in its broadest sense is a feature of virtually all neoplastic cells. In addition to the mutations and/or gene amplifications that appear to be a prerequisite for the acquisition of a neoplastic phenotype, human cancers exhibit other "markers" of genomic instability--in particular, a high degree of aneuploidy. Indeed, many studies have shown that aneuploidy is an almost invariant feature of cancer cells, and it has been argued by some that the emergence of aneuploid cells is a necessary step during tumorigenesis. The functional link between genomic instability and cancer is strengthened by the existence of several "genetic instability" disorders of humans that are associated with a moderate to severe increase in the incidence of cancers. These disorders include ataxia telangiectasia, Bloom's syndrome, Fanconi anemia, xeroderma pigmentosum, and Nijmegen breakage syndrome, all of which are very rare and are inherited in a recessive manner. Analysis of the cells from such cancer-prone individuals is clearly a potentially fruitful approach for delineating the genetic basis for instability in the genome. It is assumed that by identifying the underlying cause of genetic instability in these disorders, one can derive valuable information not only about the basis of particular genetic diseases, but also about the underlying causes of genomic instability in sporadic cancers in the general population. In this article, we review the clinical and cellular properties of genetic instability disorders associated with cancer predisposition. In particular, we focus on the rapid advances made in our understanding of these disorders that have derived from the cloning of the genes mutated in each case. Because in many instances the affected genes have analogs in lower eukaryotic species, we shall discuss how studies in yeasts in particular have proved valuable in our understanding of human diseases and predisposition to cancer.

Genetic instability in patients with Hodgkin's disease undergoing chemotherapy

We have studied the effect of chemotherapy on the level of a particular kind of genetic instability in patients with Hodgkin's disease. The particular type of genetic instability assayed is exemplified by trans-rearrangements between two (rather than within one) T cell antigen receptor. 16 patients were studied during their course of treatment. Presentation samples were available for 13 of these patients; 9 of them showed an increase in the level of trans-rearrangements during their exposure to chemotherapeutic agents (P < 0.043). All patients for whom posttherapy samples were available (10 out of 16) showed a return to baseline levels of trans-rearrangements 1-5 mo after completion of therapy (P < 0.03). Thus, this assay appears to be a marker for the "destabilizing" effects of certain chemotherapeutic agents.